P0400: Exhaust Gas Recirculation Flow Malfunction

P0400 means the engine control unit has detected that exhaust gas recirculation flow is not within the expected range. The EGR system recirculates a portion of exhaust gas back into the intake to lower combustion temperatures and reduce NOx emissions. A blockage or valve failure disrupts this flow.

P0400 è un codice diagnostico di guasto relativo a emissioni, classificato con gravità moderate. Quando la centralina (ECU) del tuo veicolo rileva questa condizione, memorizza P0400 e accende la spia motore.

Se il tuo veicolo ha attivato P0400, potresti notare uno o più di questi sintomi:

• Check engine light on
• Rough or unstable idle
• Engine knocking or pinging under load
• Reduced fuel economy
• Failed emissions test (high NOx readings)
• Hesitation during acceleration

Ecco le cause più comuni di P0400, ordinate in base alla probabilità che siano la causa del problema:

In genere sì, per brevi tragitti. The vehicle is generally safe to drive in the short term, but EGR faults can cause increased NOx emissions, rough idle, and reduced fuel economy. Repair before the next emissions inspection.

Segui questi passaggi per individuare la causa principale di P0400:

1. Check for companion EGR codes (P0401, P0402, P0403) that may help narrow down whether the issue is insufficient flow, excessive flow, or an electrical fault
2. Remove the EGR valve and visually inspect for carbon buildup. A heavily clogged valve is the most common cause and can be cleaned with carburettor cleaner
3. With the EGR valve removed, inspect the intake and exhaust passages for carbon blockage. Use a flashlight and probe to check passage diameter
4. Test the EGR valve operation by applying vacuum (vacuum-operated) or commanding it open with a scan tool (electronic). It should open and close smoothly
5. If the valve operates correctly, check the DPFE sensor or EGR position sensor readings on the scan tool against manufacturer specifications

I costi di riparazione di P0400 variano a seconda della causa principale e del tuo veicolo. Ecco le stime tipiche:

P0400 si comporta in modo diverso a seconda del tuo veicolo. Seleziona la tua auto qui sotto per cause specifiche del modello, problemi noti e stime dei costi adeguate:

Questi codici compaiono spesso insieme a P0400 o indicano problemi correlati: